Coupling device for introducing acoustic waves into the body of a life form

ABSTRACT

The invention is directed to a coupling device for introducing acoustic waves into the extremity of a life form, said coupling device comprising a rigid, hollow-cylindrical outside part as the entry wall for the acoustic waves, a flexible hose section coaxially arranged in the outside part as the exit wall, and a propagation medium for the acoustic waves which fills the annular space between outside part and hose section.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention is directed to a coupling device for introducing acousticwaves into the body of a life form.

2. Description of the Prior Art

Acoustic waves are introduced into the body of life forms both fordiagnostic as well as for therapeutic purposes, such as in apparatusesfor ultrasound diagnostics and extracorporeal shock wave lithotripsy(ESWL). The acoustic waves can thereby not be directly introduced intothe body of the life form, i.e. on the basis of direct application ofthe emission surface of the ultrasound transducer or, of the shock wavesource against the body surface of the life form. On the contrary, ausually fluid propagation medium for the acoustic waves is generallyarranged between the source of the acoustic waves.

For example, it can thus be provided that the source of acoustic wavesis introduced into the wall of a bath containing the propagation mediumwherein the patient is seated such that the patient assumes therespectively required position relative to the source of the acousticwave. Apart from the fact that it involves substantial technologicaloutlay, this solution is hygienically problematical. A switch hastherefore been made to integrating the source of acoustic waves into ahousing filled with the propagation medium, this housing comprising anexit window through which the generated acoustic waves can emerge. Thehousing containing the source can then be applied against the bodysurface with its exit window in such a spatial orientation that thediagnostically or, respectively, therapeutically relevant region of thebody is charged with the acoustic waves. This solution, which isreferred to as "dry coupling", unites the advantage of low technologicaloutlay with that of beneficial hygienic conditions. The exit window,moreover, can be fashioned as a flexible application pillow, with theadvantage that a contact area between the exit window and the bodysurface that is adequately large for the introduction of acoustic wavesalso derives in body regions wherein parts of the skeleton are locatedimmediately below the body surface.

The problem arises in certain cases that the source of acoustic waves,retaining the "dry coupling" with the body surface, must be particularlyautomatically adjusted relative to the body with a mechanical adjustmentmeans. For example, this is the case when the focus of the shock wavesalong the zone to be treated must be adjusted in the treatment of boneconditions in the region of the extremities with focused shock waves,this, for example, potentially making it necessary that the shock wavesource be conducted around the extremity in a swivel motion. In thesecases, a technologically complicated and expensive adjustment mechanismmust be provided for the source of acoustic waves even when the exitwindow is executed as a flexible application pillow, since it canotherwise not be assured that the contact area between exit window andbody surface is adequately large in order to guarantee a good acousticcoupling.

German OS 35 03 702 discloses a "dry" coupling device having an exitwindow formed by a flexible, stretchable hose section arrangedconcentrically in the outside part which, together with the outsidepart, limits an annular space filled with a propagation medium. In thisknown device, however, the outside part does not constitute an entrywall for the acoustic waves. Instead, the outside part is provided withan opening into which a shockwave source is introduced.

SUMMARY OF THE INVENTION

The invention is based on the object of specifying a coupling device foracoustic waves which makes it possible in a simple and cost-beneficialway to adjust, particularly to automatically adjust a source of acousticwaves relative to the body into which acoustic waves are to beintroduced given "dry coupling" upon constant retention of a goodacoustic coupling.

This object is inventively achieved by a coupling device for introducingacoustic waves into the body of a life form which comprises:

a) an entry wall for the acoustic waves which is formed by an outsidepart comprising a rigid, rotationally symmetrical, outer surface;

b) an exit wall for the acoustic waves which is formed by a flexible,stretchable hose section concentrically arranged in the outside part,whereby the hose section together with the outside part limits anannular space; and

c) a propagation medium contained in the annular space for the acousticwaves.

As a consequence of the fact that the outer surface of the entry wall isfashioned rotationally symmetrical, the source of the acoustic waves canbe conducted around the coupling device on a circular path and, forexample, around an extremity accepted therein and on a circular patharound that axis with respect whereto the outer surface is rotationallysymmetrical, without having the contact area of the exit window or,coupling cushion of the source of acoustic waves to the outer surface ofthe entry wall changing to a noteworthy degree. As a consequence of thefashioning of the exit wall as a flexible hose section, moreover, it isguaranteed that this lies flush against the entire circumference of thebody or, respectively, body part into which the acoustic waves are to beintroduced. It thus becomes clear that, first, a good acoustic couplingis always assured between the coupling cushion of the source of acousticwaves and the entry wall of the coupling device and, on the other hand,between the exit wall of the coupling device and the body or body part,so that the acoustic waves can be introduced into the body or into thebody part with the lowest possible losses. Moreover, the adjustment ofthe source of acoustic waves relative to the body or to the body parttakes on an extremely simple configuration since this--as a consequenceof the interposition of the coupling device comprising a rotationallysymmetrical, outer surface--can ensue on a circular path, whichsubstantially simplifies an automatic adjustment of the source of theacoustic waves.

It is provided in a preferred embodiment of the invention that the outersurface of the outside part is cylindrically fashioned. On the basis ofcombining a circular motion around the center axis of the generatedsurface and a straight-line motion parallel to the center axis of thegenerated surface, it then becomes possible in a simple way to align thesource of acoustic waves nearly arbitrarily relative to the body or,respectively, body part accepted in the coupling device within thelimits established by the dimensions of the coupling device.

In the preferred embodiment the volume of the annular space and thequantity of propagation medium contained therein are variable. Theinside diameter of the hose section provided as exit wall can thus bevaried by varying the amount of propagation medium contained in theannular space, this yielding the advantage that the flush application ofthe hose section against the surface of the body or of the body partrequired for a good acoustic coupling can always be realized for bodiesor body parts having different circumferences.

In order to keep the acoustic losses that arise due to the insertion ofthe coupling device between the source of acoustic waves and the body orthe body part as low as possible, one version of the invention providesthat the acoustic impedances of the propagation medium, of the materialof the outside part and of the material of the hose section at leastessentially coincide. No noteworthy losses due to reflection then ariseat the boundary surfaces between outside part and propagation medium andbetween propagation medium and hose section. The losses can be furtherreduced when the acoustic impedances of the propagation medium, thematerial the outside part and of the material of the hose section atleast essentially coincide with that of animal, particularly humantissue, since no noteworthy reflections then occur either at theboundary surface between the hose section and the surface of the body orbody part. Acoustic impedances that largely coincide with human tissueare present when water is provided as acoustic propagation medium, atleast one material from the group of ethylene-propylene-diene andpolymethylene--EPDM--rubber, polymethylpentene (TPX), polystyrol isprovided as material of the outside part and at least one material fromthe group of EPDM rubber, Latex, polyvinylchloride (PVC) is provided asmaterial of the hose section.

DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is shown in a highly schematiclongitudinal section in the attached drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coupling device of the invention shown in the figure and referenced1 overall serves the purpose of acoustically coupling a schematicallyindicated shock wave source 2 for the treatment of a bone condition, forexample a poorly healing fracture due to inadequate callus formation, toa human extremity 3, for example a thigh. For treatment, focused shockwaves generated with the shock wave source 2 (as used herein"shockwaves"0 means acoustic pressure pulses having an extremely steepleading edge) are introduced into the extremity 3 through the couplingdevice 1. As exit window for the shock waves, the shock wave source 2comprises a flexible application cushion 21 pressing against thecoupling device 1. For example, U.S. Pat. No. 4,674,505 discloses such ashock wave source. For treating the fracture, the focus F of the shockwaves must be moved along the fracture gap 4 of the fracture. The bone Kto be treated is shown unsectioned in the figure.

As the entry wall for the shock waves, the coupling device 1 of theinvention comprises a rigid, cylindrical tube-shaped outside part 5 thatis fabricated of a material, for example EPDM rubber, polymethylpentene(TPX) or polystyrol whose acoustic impedance essentially corresponds tothat of human tissue and that only slightly attenuates the shock waves.Further, the coupling device 1 comprises a flexible hose part 6 that ismanufactured of a stretchable material, for example EPDM rubber, Latexor polyvinylchloride (PVC) that only slightly attenuates shock waves andhas an acoustic impedance essentially corresponding to that of humantissue. As the exit wall for the shock waves, the hose part 6 comprisesa hose section 7 each of whose ends merges into a radially outwardlyextending bead part 8, 9, whereby the free edges of the bead parts 8, 9of the hose part 6 are connected liquid-tight, for example by gluing, tothe outside part 5 along the respectively corresponding edge of thecylindrical, outer generated surface of the outside part 5. The hosepart 6 has an increased wall thickness in the region of the bead parts8, 9. A schematically indicated fabric 10, 11 that can be fabricated,for example, of nylon thread is also respectively embedded into the beadparts 8, 9. What is thereby achieved is that the hose part 6 is in factflexible but not stretchable in the region of the bead parts 8, 9.

The annular space limited by the outside part 5 and by the hose part 6having the hose section 7 and the bead parts 8, 9 is filled with a fluidas propagation medium for the shock waves generated with the shock wavesource 2, the acoustic impedance thereof essentially corresponding tothat of human tissue. For example, water is suitable as propagationmedium. In order to be able to fill the annular space with water, a hose12 is attached to the bead part 9, the end of said hose 12 beingprovided with a schematically indicated coupling part 13a and aschematically illustrated shut-off valve 14 being connected therein. Thecoupling part 13a is a component of a coupling 13 whose second couplingpart 13b is provided at the end of a line 15 that leads to a reservoir16 containing water which, as the line 15, is schematically shown. Thespace located above the water level in the reservoir 16 is incommunication with a schematically indicated pressure source 17, forexample a compressed air bottle, and can be charged with a valve 18 withan adjustable pressure that is elevated in comparison to the ambientpressure. A further valve 19, which is schematically shown as is thevalve 18, is connected between the pressure source 17 and the reservoir16, this further valve 19 making it possible to optionally connect theinterior of the reservoir 16 to the pressure source 17 or to thesurrounding atmosphere via an aeration line 20.

For the implementation of a treatment, the hose 12 is first connected bythe coupling 13 to the unpressurized reservoir 16 and the shut-off valve14 is opened. Insofar as the water located in the annular space is undera pressure which is elevated in comparison to the ambient pressure, thiswater flows into the reservoir 16. This leads to the fact that the hosepart 6 assumes its initial shape indicated with broken lines in thefigure, the hose section 7 therein having a hollow-cylindrical shape andthe bead parts 8, 9 having an approximately U-shape in cross section.The extremity 3 to be treated is now introduced into the coupling device1 or the coupling device 1 is pushed onto the extremity 3 to be treated.When, differing from what is shown in the figure, the extremity 3 to betreated has an outside diameter that is larger than the inside diameterof the hose section 17 in its initial shape, water is thereby expressedback into the reservoir 16. For improving the acoustic coupling, theextremity 3 to be treated can potentially be coated with awater-containing gel before the application, as is likewise employed inthe implementation of ultrasound examinations. When the extremity 3assumes the desired position in the coupling device 1, the fracture asviewed in longitudinal direction of the extremity 3 being preferablylocated centrally between the ends of the coupling device 1 in thisdesired position, the reservoir 16 is charged with a pressure matched tothe respective treatment by an appropriate actuation of the valve 20,this pressure being adjustable with the valve 18. Water is therebypressed from the reservoir 16 into the annular space, with the resultthat the flexible and stretchable hose section 7 of the hose part 6presses flush against the extremity 3. When the desired pressure ispresent, the coupling 13 can be released after the closing of theshut-off valve 14 and after the reservoir 16 has been switchedunpressurized with the valve 20 and the extremity 3 to be treated can beseated such that the coupling device 1 is accessible to the shock wavesource 2 in the region of the entire, outer generated surface of theoutside part 5. It is thereby expedient when the coupling device 1 isfixed in the corresponding position with the assistance of retainermeans and in a way that is not shown. In this position, the shock wavesource 2 has its flexible application cushion 21 pressing against theouter surface of the outside part 5 of the coupling device 1, whereby itis expedient to coat the application cushion 21 and/or the outer surfaceof the outside part 5 with a water-containing gel for improving theglide behavior and the acoustic coupling.

Since it has been shown that charging a fracture with focused shockwaves induces callus formation or bone growth, the focus F of the shockwaves generated with the shock wave source 2 is moved along the entirefracture gap 4 for treating the fracture. To this end, the shock wavesource 2, with a constant emission of shock waves, is gradually movedaround the extremity 3 with constant application of the applicationcushion 21 against the outer surface of the outside part 5. It mustthereby be simultaneously assured on the basis of corresponding,additional adjustment motions that the focus F of the shock waves isalways essentially located in the region of the boundary surface betweenthe bone and the tissue surrounding it. In the case of the couplingdevice of the invention, this can be achieved in a technologicallysimple way. Since the outer surface of the outside part 5 of thecoupling device 1 is cylindrically fashioned, namely, it is assured thatthe acoustic axis A of the shock wave source 2 on which the focus F ofthe shock waves lies always intersects the center axis M of the couplingdevice 1 during the treatment. On the basis of a simple circular motionof the shock wave source around the center axis M and on the basis of alikewise simple, straight-line displacement of the shock wave sourceparallel to the center axis M, it can thus be achieved that the acousticaxis A intersects the fracture gap 4 for arbitrary positions of theshock wave source 2 on the circular path. In order to guarantee that thefocus F of the shock waves lies in the boundary surface between bone andsurrounding tissue in the required way, the focus F must merely bedisplaced as required in a known way along the acoustic axis A. It thusbecomes clear that the coupling device 1 of the invention makes itpossible to adjust the focus F of the shock waves along the fracture gap4 on the basis of adjustment motions of the shock wave source 2 that canbe technologically realized in a simple way. This occurs with theassistance of a locating means (not shown in the figure) that canoperate on an x-ray and/or ultrasound basis in a known way. The acousticcoupling of the shock wave source 2 to the extremity 3 to be treated isalways of the same quality regardless of the position of the shock wavesource 2 relative to the extremity 3 since, on the one hand, the contactarea between the application cushion 21 of the shock wave source 2 andthe coupling device 1 is always of the same size as a consequence of thecylindrical shape of the outer surface of the outside part 5 and, on theother hand, a flush application of the coupling device 1 against theextremity to be treated is always assured as a consequence of theflexible and elastic properties of the hose section 7.

The outer surface of the outside part 5 need not necessarily becylindrically fashioned. Other rotationally symmetrical shapes, forexample a spherical shape, also come into consideration.

The exemplary embodiment which has been set forth is directed to thetreatment of a bone condition. The coupling device of the invention,however, can also be employed in other therapeutic and/or diagnosticmedical procedures.

We claim as our invention:
 1. Coupling device for use with means forgenerating acoustic waves for introducing said acoustic waves into thebody of a life form, comprising:a) an entry wall for acoustic wavesformed by an entry wall part having a rigid, rotationally symmetrical,outer surface adapted to abut said means for generating acoustic waves;b) an exit wall for the acoustic waves formed by a flexible, stretchablehose section concentrically arranged within the entry wall part, andsidewalls connecting said hose section and said entry wall part, thehose section together with the entry wall part and said sidewallslimiting an annular space therebetween; and c) a propagation medium forthe acoustic waves contained in the annular space, said entry wall, saidpropagation medium and said exit wall being oriented relative to eachother end to said means for generating acoustic waves and to the body ofsaid life form so that said acoustic waves pass sequentially throughsaid entry wall said propagation medium and said exit wall whenpropagating from said means for generating acoustic waves to the body ofsaid life form.
 2. Coupling device according to claim 1, wherein theouter surface of the outside part is cylindrical.
 3. Coupling deviceaccording to claim 1 or 2, further comprising means for varying thevolume of the annular space and the amount of propagation mediumcontained therein.
 4. Coupling device according to claim 1, wherein thepropagation medium, the material of the outside part, and the materialof the hose section have respective acoustic impedances, said acousticimpedances being substantially the same.
 5. Coupling device according toclaim 4, wherein the acoustic impedances of the propagation medium, thematerial of the outside part, and the material of the hose section aresubstantially the same as human tissue.
 6. Coupling device according toclaim 1, wherein the propagation medium consists of water.
 7. Couplingdevice according to claim 1 wherein said outside part consists of atleast one material selected from the group consisting ofethylene-propylene-diene and polymethylene (EPDM) rubber,polymethylpentene (TPX), and polystyrol.
 8. Coupling device according toclaim 1 wherein said hose section consists of at least one materialselected from the group consisting of ethylene-propylene-diene andpolymethylene (EPDM) rubber and polyvinylchloride (PVC).
 9. An apparatusfor treating a life form with acoustic waves comprising:a shockwavesource having an exit window, said shockwave source generatingshockwaves which exit said shockwave source through said exit window;and coupling means for coupling said shockwaves from said exit window ofsaid shockwave source into the body of said life form, said couplingmeans including an entry wall for the acoustic waves adapted forabutment against said exit window of said shockwave source, said entrywall being formed by a part having a rigid, rotationally symmetricalouter surface, an exit wall for the acoustic waves formed by a flexible,stretchable hose section concentrically arranged within said part ofsaid entry wall and connected thereto by sidewalls, the hose sectiontogether with the part of the entry wall and the sidewalls limiting anannular space therebetween, and a propagation medium for the acousticwaves contained in the annular space,said entry wall, said propagationmedium and said exit wall being oriented relative to each other and tosaid shockwave source and to the body of said life form so that acousticwaves pass sequentially through said entry wall, said propagation mediumand said exit wall when propagating from said exit window to the body ofsaid life form.